1. Field of the Invention
The present invention relates to a drive circuit system for driving a motor for opening and closing a power window.
2. Description of the Related Art
A control switch for opening and closing a power window on the side of a driver's seat in an automobile is capable of selecting any of 1) a neutral position, 2) an opening position, 3) an automatic opening position, 4) a closing position and 5) an automatic closing position. If the control switch is moved to the opening position or the closing position, the motor is driven only for a period of time that the position is maintained, thereby opening or closing the power window. When the control switch is initially moved to the automatic opening position or the automatic closing position, the driving of the motor is automatically continued until the power window is fully opened or closed, even if the control switch is thereafter returned to the neutral position.
First, a prior art drive circuit system for a power window will be described below with reference to FIG. 1. A control switch S operated by a driver, an opening relay Ro adapted to be closed when the power window is opened and a closing relay Rs adapted to be closed when the power window is closed, are connected between a) a first line L.sub.1, connected to a power source 1, comprising a battery of 12 volts mounted on a vehicle, and b) a second line L.sub.2 connected to a ground of 0 volts. The control switch S includes a contact 3 biased toward a neutral position by a spring which is not shown. The contact 3 is capable of being connected to an opening terminal 4o, a closing terminal 4s, an automatically opening terminal 4ao and an automatically closing terminal 4as when moved by an operator.
An electronic circuit E detects five operated positions of the control switch S and controls the opening and closing of the opening relay Ro and the closing relay Rs depending upon the position of the contact 3. When the control switch S is moved to the opening position to connect the contact 3 to the opening terminal 4o, a coil 5o of the opening relay Ro is energized, whereby a contact 6o is separated from an OFF terminal 7o and connected to an ON terminal 8o. As a result, a circuit is formed and consists of the power source 1, the first line L.sub.1, the ON terminal 8o of the opening relay Ro, the contact 6o, a third line L.sub.3, the motor 9, the third line L.sub.3, the contact 6.sub.s of the closing relay Rs and the OFF terminal 7s, the second line L.sub.2 and ground 2. Thus, the motor 9 is driven in an opening direction to open the power window.
When the control switch S is moved to the closing position to connect the contact 3 to the closing terminal 4s, the coil 5s of the closing relay Rs is energized, whereby the contact 6s is separated from the OFF terminal 7s and connected to the ON terminal 8s. As a result, a circuit is formed and consists of the power source 1, the first line L.sub.1, the ON terminal 8s of the closing relay Rs and the contact 6s, the third line L.sub.3, the motor 9, the third line L.sub.3, the contact 6o of the opening relay Ro and the OFF terminal 7o, the second line L.sub.2 and ground 2. Thus, the motor 9 is driven in a closing direction to close the power window.
When the control switch S is moved to the automatically opening position or automatically the closing position to connect the contact 3 to the automatically opening terminal 4ao or the automatically closing terminal 4as, the electronic circuit E energizes the coil 5o of the opening relay Ro or the coil 5s of the closing relay Rs to drive the motor 9 in the opening or closing direction. When the motor 9 is initially driven, the driving of the motor 9 is continued by the electronic circuit E, even if the control switch S is returned to the neutral position. The electronic circuit E, which receives a signal from the rotative pulser 11 which is mechanical connected to a rotary shaft of the motor 9, deenergizes the coil 5o of the opening relay Ro or the coil 5s of the closing relay Rs to stop driving the motor 9, when the electronic circuit E detects that the power window has reached the fully opened or closed position.
If an object is caught between a window frame and a window pane during driving of the power window in the closing direction, the load of the motor 9 is increased. The electronic circuit E detects that an object is caught from an electric current of the motor 9. As a result, the electronic circuit E opens the closing relay Rs and closes the opening relay for a predetermined period of time, thereby driving the power window slightly in the opening direction to prevent the object from being caught.
In the above prior art drive circuit system, if the opening relay Ro is closed by energization of the coil 5o of the opening relay Ro due to a current leakage when the electronic circuit E becomes wet due to water entering the circuit E or due to water condensation, there is a possibility that the power window is inadvertently opened. Reversely, if the closing relay Rs is closed by energization of the coil 5s of the closing relay Rs due to a current leakage, there is a possibility that the power window is inadvertently closed.